Doesn’t look like a Nav hand controller to me, unless it predates me...
The F3 rear seat one, later adopted by the GR4, was this one (auction nothing to do with me):
https://www.ebay.co.uk/p/19022896273
From memory it might be one of the flare/chaff/BOL IR dispensers that were next to the canopy on either side in the rear seat?